Surface crosslinked and surfactant coated absorbent resin particles and method of preparation

Abstract

The invention is surface crosslinked particles of water absorbing resin comprising particles of a carboxyl containing water-absorbent resin; wherein the particles of the carboxyl containing water-absorbent resin are crosslinked at or near the particle surface by a polyhydroxy compound capable of reacting with the carboxyl moieties of the water-absorbent resin, and the particles have coated on or bound to the surface a nonionic surfactant having an HLB of from 3 to 10. Additionally a process for the preparation of such surface crosslinked and surfactant coated absorbent resin particles is disclosed. Further disclosed is a water-absorbent structure comprising a synthetic or natural fiber or paper based woven or nonwoven carrier structure and surface crosslinked and surfactant coated water-absorbent resin particles of this invention.

We claim: 
     
       1. Surface crosslinked particles of water-absorbent resin comprising a crosslinked carboxyl containing, solution polymerized, water-absorbent resin wherein the resin comprises a polymer of acrylic or methacrylic acid in which from about 50 to about 99 percent of the carboxyl moieties are neutralized; wherein the crosslinked carboxyl containing water-absorbent resin is crosslinked at or near the particle surface by a nonionic surfactant which is a polyethoxylated sorbitol-lanolin derivative having an HLB of from 3 to 10, in the presence of from about 0.01 to about 10 parts by weight of a polyhydroxy compound based on 100 parts of the water-absorbent resin, the polyhydroxy compound being capable of reacting with the carboxyl moieties which is glycerol or sorbitol and the water-absorbent resin particles have coated or bound on their surface from about 0.01 to about 2.0 parts by weight of the surfactant based on 100 parts of the water-absorbent resin the nonionic surfactant. 
     
     
       2. A process for the preparation of surface crosslinked absorbent resin particles which comprises A) contacting particles of a hydrogel of crosslinked carboxyl containing water-absorbent resins with a nonionic surfactant having an HLB of from 3 to 10, optionally in the presence of a composition comprising a polyhydroxy compound which is ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerol, polyglycerol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, propane diol butane diol, diethanolamine, triethanolamine, trimethylolpropane, pentaerythritol, sorbitol or mannitol, optionally water and optionally a water miscible polar solvent, under conditions such that the surfactant and optionally the polyhydroxy compound, coat the water-absorbent resin particles without significant penetration into the interior of the absorbent resin particles;   B) drying the mixture of the hydrogel of the water-absorbent resin, and composition containing the surfactant and optionally the polyhydroxy compound, under conditions such that the water, and optional solvent if present, are removed and the surfactant and optionally the polyhydroxy compound does not significantly react with the carboxyl moieties of the water-absorbent resin;   C) optionally, reducing the particle size of the dried coated absorbent resin by mechanical means; and   D) heating the coated water-absorbent resin particles under conditions such that the surfactant and optionally the polyhydroxy compound react with the carboxy moieties of the water-absorbent resin so as to crosslink the surface of the water-absorbent resin particles.   
     
     
       3. A process according to claim 2 wherein the composition containing the polyhydroxy compound and surfactant comprises i) from about 0 to about 99 parts by weight water;   ii) from about 0 to about 99 parts by weight polar organic solvent;   iii) from about 0.1 to about 99 parts by weight of surfactant;   iv) from about 1 to about 99 parts by weight of polyhydroxy compound.   
     
     
       4. A process according to claim 3 wherein from about 50 to about 99.98 parts of water-absorbent resin hydrogel by weight and from about 0.02 to about 50 parts by weight of the solution containing the polyhydroxy compound and surfactant, are contacted. 
     
     
       5. A process according to claim 4 wherein A) the hydrogel of the water-absorbent resin and the composition comprising polyhydroxy compound and surfactant, are contacted for a time of from about 0.5 minutes to about 10 minutes at a temperature of from about 20° C. to about 150° C.;   B) the mixture of the hydrogel of water-absorbent resin having coated thereon the composition comprising polyhydroxy compound and surfactant, are dried at from about 100° to about 175° C. for about 10 to about 60 minutes;   C) the particle size of the dried coated water-absorbent resin particles is reduced to less than about 2 mm;   D) the coated water-absorbent resin particles are heated to a temperature of from about 175° to about 210° C. for from about 5 to about 75 minutes such that the polyhydroxy compound reacts with the carboxyl moieties at or near the surface of the water-absorbent resin particles to crosslink the water-absorbent resin particles at or near the surface.